Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> writes: > On Tue, 3 Jul 2018 at 04:57, Alexander Shishkin > <alexander.shishkin@xxxxxxxxxxxxxxx> wrote: >> >> On Tue, Jul 03, 2018 at 01:03:48PM +0300, Alexander Shishkin wrote: >> > On Mon, Jul 02, 2018 at 04:33:29PM -0600, Mathieu Poirier wrote: >> > > +/* >> > > + * PMU driver configuration works the same way as filter management above, >> > > + * but without the need to deal with memory mapping. Driver configuration >> > > + * arrives through the SET_DRV_CONFIG ioctl() where it is validated and applied >> > > + * to the event. When the PMU is ready it calls perf_event_drv_config_sync() to >> > > + * bring the configuration information within reach of the PMU. >> > >> > Wait a second. The reason why we dance around with the generations of filters >> > is the locking order of ctx::mutex vs mmap_sem. In an mmap path, where we're >> > notified about mapping changes, we're called under the latter, and we'd need >> > to grab the former to update the event configuration. In your case, the >> > update comes in via perf_ioctl(), where we're already holding the ctx::mutex, >> > so you can just kick the PMU right there, via an event_function_call() or >> > perf_event_stop(restart=1). In the latter case, your pmu::start() would just >> > grab the new configuration. Should also be about 90% less code. :) >> >> Also, since it affects the AUX buffer configuration, it is probably a one >> time ioctl command that you issue before you mmap the buffer. If that's >> the case, you don't even have to worry about stopping the event, as it >> shouldn't be running, because without the buffer perf_aux_output_begin() >> should fail and so should the pmu::add() iirc. >> > > The idea behind the current approach was to make the SET_DRV_CONFIG > ioctl() usable by other drivers where multiple ioctl() calls could be > performed while a session in ongoing. I also opted to introduce a > _sync() function to let the PMU refresh its configuration at the time > of its own choosing rather than having to interrupt the session. Yes, but the times of PMU's own choosing would still be more or less limited to ->start()/->stop(). You can also do an event_function_call(), which would call ->config_sync(), which would be free to decide what to do with the new information, up to and including doing a ->stop()/->start() sequence. My guess is that you'd want to do either of the following: * decide to apply the new configuration immediately, and do the start-stop thing, * decide to defer the new configuration until the next ->start(). Both should work via cross call directly from the ioctl() call. > But all I need for coresight is to have available the sink information > and PMU configuration (in an upcoming patchset) by the time > setup_aux() is called. You are correct, this is a one time > configuration and since the event isn't running there is no need for > locking - I should be able to access the PMU when the ioctl is called. > > If you are fine with this bare-bone scenario and don't care much about > usability in different situation, I'll do a respin with minimal > functionality that cover my needs. It doesn't have to be bare-bones, what I'm saying is that you shouldn't need the event->drv_config, as you can directly call pmu::config(new_config) (or config_sync(), but I'm guessing the _sync part is redundant if you don't keep the configuration in 2 parts) from the ioctl() and it should cover all your bases. Regards, -- Alex -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
